A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, multimedia content, and other data. A session may, for example, be a telephone call type session between two users, a multi-party session, for example a conference call, or a data communication session between at least one user and a node such as an application server (AS).
A communication system typically operates in accordance with given standards and/or specifications, which set out what the various entities associated with the communication system are permitted to do and how that should be achieved. For example, a standard or specification may define if the user, or more precisely, user equipment is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters, which shall be used for the connection may also be defined. In other words, a specific set of rules on which the communication can be based is defined to enable communication. A communication system may provide fixed or wireless access for the user equipment. A communication system may include various entities for controlling and/or carrying communications between two or more communicating parties. Different control entities may be interconnected. One or more gateway nodes may be provided for connecting various networks, for example for connecting a public switched telephone network (PSTN), a public landline mobile network (PLMN), a local area network (LAN), a wireless LAN (WLAN) and/or other communication networks such as an IP (Internet Protocol) and/or other packet switched data networks to each other. A communications network the user is connected to is understood as providing an access system enabling a user to access other networks, hosts, or services offered by specific service providers.
In a packet data network, a packet data carrier may be established to carry traffic flows consisting of data packets over the network. Each data packet is provided with appropriate routing information, such as destination address and port information so that the various entities in the route to the destination know where the data packet shall be forwarded.
Various types of services can be provided to the users of a communications system. A type of possible services is commonly referred to as multimedia. An example of multimedia services is where multimedia content, such as images, videos, audio files or other data, may be downloaded from an application server to a user equipment. Users may also send data to other entities via a communication system. For example, a user may create something, such as take a photo or make a video, and send his creation in a digitized form, i.e. as content data to a multimedia server. The work may then be downloaded from the server by other parties interested of the same subject. Data communications for enabling communication of multimedia may be provided by an appropriate data communications system, for example an Internet Protocol Multimedia system.
A multimedia data communication system may comprise an addresses translator node, for example a network address translator (NAT). Use of an address translator results a situation where a pair of a private Internet Protocol (IP) address and a port that belongs to an internal node behind an address translator node translates to a different pair of a public IP address and a port.
In an IP multimedia session (IMS) the IP address and port used for sending and receiving a media packet is usually different than the IP address and port used to send and receive the signalling traffic. The presence of the address translator node therefore may cause certain problems for a node that is located behind the address translator node. For example, because of the intermediate address translator node such a node may not know the translation of private and public IP address and port pairs for incoming media traffic in advance, for example before it sends a media packet through the address translator node.
An element known as the media proxy may also be provided in a multimedia system. The function of a media proxy is to force the media traffic between parties, e.g. a user and an application server, to traverse through it to provide the network operator with a better control on the media traffic. The media proxy reserves a pair of public IP address and port to be used by a node for the media traffic, and maps this pair of reserved public IP address and port to the IP address and port of the node.
The presence of a media proxy may complicate the already complicated situation caused by an address translator node even further. If one of the parties is behind an address translator node, the media proxy must map the public IP address and port of the party to the reserved IP address and port. The presence of an address translator node would require the media proxy to map the translated IP address and port for media packets instead of the private IP address and port of the party to the reserved IP address and port reserved by the media proxy. However, this translated IP address and port is not available in the media proxy at the time of IP address and port reservation.
On the other hand, if no address translator node is present, the media proxy can instantly map the IP address and port of the node to the IP address and port reserved by the media proxy. In other words, the presence of an address translator node necessarily affects the behavior of a media proxy.
A problem is the lack of a proper mechanism to inform and/or control the media proxy in this regard, and it is the aim of the embodiments of the present invention to address or at least mitigate this and other problems caused by the presence of an address translator.